I. Field of the Invention
This invention relates to a process for the reactivation of a catalyst comprised of iridium, or an admixture of iridium with another metal, or metals, especially platinum. In particular, the invention relates to a process for the reactivation of a catalyst, or bed of catalyst, comprised of a composite of a porous inorganic oxide support, particularly alumina, and an iridium metal or admixture of said metal with other metals, particularly platinum, or admixture of iridium and platinum with another metal, or metals, which has been deactivated by coke deposits thereupon.
II. Background and Prior Art
The petroleum industry has been commercially employing reforming, or hydroforming processes for upgrading virgin or cracked naphthas to produce high octane products for many years. In reforming, a dual-functional catalyst, or catalyst having an acid function and hydrogenation-dehydrogenation function, is employed. A metal component, or components, is substantially atomically dispersed upon the surface of a porous, inorganic oxide support, notably alumina, to provide the necessary hydrogenation-dehydrogenation function. Platinum catalysts, particularly metal promoted platinum catalysts, are currently employed, reforming being defined as the total effect of the molecular changes, or hydrocarbon reactions, produced by dehydrogenation of cyclohexanes and dehydroisomerization of alkylcyclopentanes to yield aromatics; dehydrogenation of paraffins to yield olefins; dehydrocyclication of paraffins and olefins to yield aromatics; isomerization of n-paraffins; isomerization of alkylcycloparaffins to yield cyclohexanes; isomerization of substituted aromatics; and hydrocracking of paraffins to produce gas and coke, the latter being deposited on the catalyst.
The activity of the catalyst gradually declines in reforming due to the build-up of carbonaceous deposits, or coke, on the catalyst which physically blocks the catalytically active metal and acidic sites. During operation, the temperature of the process is gradually raised to compensate for the activity loss. Eventually, however, economics dictates the necessity of reactivating the catalyst. Consequently, in all processes of this type the catalyst must necessarily be periodically regenerated by burning off the coke at controlled conditions. In the regeneration of unpromoted platinum catalysts the technique of reactivating the catalyst has required catalyst regeneration, or burning of the coke from the catalyst, this step being followed by redispersing the agglomerated metal by halogen treatment. For example, coke can be readily burned from a coked platinum catalyst by contact with an atmosphere of oxygen, or oxygen and chlorine gas, at flame front temperatures of about 540.degree. C., and oxygen concentrations up to about 6 volume percent. The agglomerated metal can then be readily redispersed to bring the activity of the catalyst essentially back to that of a fresh catalyst. Thus, the agglomerated platinum metal is redispersed to a fine state of dispersion, with relative ease, by treatment with chloride or other halogen-containing reagent, generally used in admixture with oxygen at elevated temperatures to increase the rate of redispersion. However, not so with iridium containing, or iridium promoted platinum catalysts. At such conditions the iridium component is severely agglomerated, and the catalyst easily damaged. Iridium once agglomerated is very difficult to redisperse, and the agglomerated iridium causes carbon or coke to be retained on the catalyst. Increasing the chloride level of an iridium containing catalyst has been found to suppress agglomeration of the iridium, but the chloride combines with the more reactive carbon to form a flameproof species of coke. Hence, the reactivation of iridium containing catalysts presents a more complex problem than presented by the earlier non iridium promoted platinum catalysts.
Techniques useful for the redispersion of platinum are not directly applicable for the redispersion of iridium, or iridium in admixture with other metal hydrogenation-dehydrogenation components. Unlike platinum, large iridium and iridium oxide crystallites are formed under the conditions at which coke is readily removed, and the platinum redispersed. Once formed, the iridium and iridium oxide crystallites are not readily redispersed to their original high surface area state by a simple halogen treatment immediately following the burning operation. Recently, faced with an acute need, techniques have been developed by virtue of which iridium, or iridium in admixture with other metal hydrogenation-dehydrogenatin components, can be redispersed to a high surface area state. Patents exemplifying the state-of-the-art of regenerating, and redispersing the iridium component of iridium containing catalysts are, e.g., U.S. Pat. Nos. 3,904,510; 3,937,660; 3,939,061; 3,939,062; 3,941,682; 3,941,716; 3,943,052; 3,981,823; 3,998,755; 4,018,670; 4,046,673; 4,148,749; 4,172,817; 4,277,369; and 4,359,400. Other patents, issued by foreign governments, are GB 2,091,577A; DDR 150,986; DDR 149,846; DDR 151,556; and European patent application No. 0093621.
III. Objects
It is an object of the present invention to provide a process for the regeneration, and reactivation, of catalysts comprised of a composite of a porous inorganic oxide support and iridium, or iridium in admixture with one or more other metals, especially platinum, which have become deactivated by contact with a hydrocarbon feed at process conditions, or deactivated by burning coke from the coked catalyst, or both.
A specific object is to provide a process wherein a catalyst comprised of iridium, or admixture of iridium and another metal, or metals, especially platinum and iridium, alone or in admixture with other metals, which has become coked and thereby deactivated by contact with a hydrocarbon feed can be reactivated by burning the coke from the catalyst without agglomeration of the iridium component, and the regenerated catalyst thereby reactivated to a state approaching, or approximating that of a fresh catalyst.
A more particular object is to provide a process by virtue of which essentially all of the coke can be burned from an iridium promoted platinum catalyst without agglomeration of the iridium component of said catalyst, and the catalyst thereby reactivated (or without increase in the level of iridium agglomeration, where the catalyst is already agglomerated); but wherein, if agglomeration of the iridium component does occur during the burn the iridium agglomerates can be redispersed.
IV. The Invention
These objects and others are achieved in accordance with the present invention which embodies a process combination the sequence of steps of which include (1) a low temperature primary burn, wherein (i) the chloride level of a coked, deactivated iridium-containing catalyst is raised by contact with a dry hydrogen chloride containing gas, (ii) and coke then burned from said chlorided, iridium-containing catalyst by contact with a dry gas which contains hydrogen chloride at level sufficient to suppress iridium agglomeration at burn temperature and a level of oxygen providing temperatures which do not exceed about 425.degree. C. sufficient to remove a preponderance of the coke without agglomeration of the iridium (or without increase in the level of iridium agglomeration, where the catalyst is already agglomerated); and (2) a high temperature secondary burn, wherein the predominantly coke depleted chlorinated iridium-containing catalyst is subjected to (iii) a chlorination step wherein the catalyst is contacted with a dry hydrogen chloride containing gas sufficient to redisperse any agglomerated iridium, particularly iridium agglomerates, produced during said low temperature primary burn, if any, and raise the chloride level of the catalyst to a yet higher level for suppression of iridium agglomeration at higher temperature than 425.degree. C., (iv) residual coke is then burned from said higher chlorided, iridium-containing catalyst by contact with a dry gas which contains hydrogen chloride at level sufficient to suppress iridium agglomeration at the higher burn temperature, and a level of oxygen sufficient to provide temperatures greater than 425.degree. C., and ranging as high as about 530.degree. C., sufficient to burn the preponderance of the residual coke from the catalyst without agglomeration of the iridium (or increase in the level of iridium agglomeration, where the iridium is already agglomerated prior to initiation of the high temperature secondary regeneration sequence). Preferably, in an additional step (3) the catalyst is stripped to reduce the level of chloride by contact of the catalyst with steam, or steam and hydrogen chloride, the molar ratio of H.sub.2 O/HCl being maintained within a range of from about 80:1 to about 20:1, preferably from about 50:1 to about 30:1, to reduce the chloride content of the catalyst below about 1.0 percent, based on the weight of the catalyst, this rendering the catalyst suitable for use in a catalytic reforming run wherein the catalyst is contacted with a hydrocarbon, or naphtha feed.
In initiating the primary, or low temperature primary burn step, a bed of the iridium-containing catalyst is contacted with a non-reactive or inert gas which contains hydrogen chloride, and essentially no water. The gas should be as dry as possible, and should contain no more than about 50 parts of water, preferably about 10 parts of water, per million parts by volume (vppm) of gas. The said bed is contacted and chlorided to a level ranging from about 0.9 percent to about 1.5 percent chloride, preferably from about 1.0 percent to about 1.2 percent chloride, based on the weight of the catalyst (dry basis) if the catalyst does not already contain this level of chloride. This level of chloride has been found adequate to protect, or passivate the iridium component of the catalyst against agglomeration, or significant increase in the level of agglomeration during the low temperature burn step, if the catalyst is already partially agglomerated. Hence, after the catalyst has been adequately chlorided, the low temperature burn is initiated by contacting said bed of catalyst with a gas which contains both hydrogen chloride and oxygen, the hydrogen chloride in concentration adequate to maintain the necessary protective level of chloride on the catalyst to prevent iridium agglomeration, or increased irridum agglomeration, and the oxygen in adequate concentration to provide the desired flame front temperature for burn off of the coke. In general, the gas will contain from about 10 parts per million, by volume of said gas (vppm), to about 100 vppm hydrogen chloride, preferably from about 30 vppm to about 50 vppm hydrogen chloride, and up to about 5000 parts, preferably from about 1000 to about 5000 parts oxygen, more preferably from about 2000 parts to about 4000 parts of oxygen, based on the volume of said gas, this amount of oxygen being adequate to maintain a flame front temperature not exceeding about 425.degree. C., preferably ranging from about 375.degree. C. to a maximum of about 425.degree. C., more preferably from about 400.degree. C. to about 425.degree. C. The reaction is conducted for time sufficient for the flame front to pass through the bed and burn coke from the catalyst without agglomeration, or significant increase in agglomeration of the iridium. Generally, in the low temperature primary burn from about 60 percent to about 90 percent, preferably from about 70 percent to about 90 percent of the coke, based on the weight of the catalyst (dry basis), is removed from the catalyst.
In initiating the secondary, or higher temperature burn step, the catalyst chlorination step is conducted for the purpose of protecting the iridium component against agglomeration, or increase in the level of agglomeration, during the subsequent higher temperature burn. The catalyst is chlorinated by contact of the catalyst with a hydrogen chloride containing gas in the absence of water, which means that the hydrogen chloride containing gas should be as dry as possible, or in no event should the gas contain moisture at a level greater than about 50 parts of water, preferably greater than about 10 parts of water, per million parts by volume of the gas. In general, the gas used to carry out the catalyst chlorination step will contain up to about 5000 parts, preferably from about 100 parts to about 5000 parts of hydrogen chloride, more preferably from about 400 parts to about 3000 parts of hydrogen chloride, per million parts by volume of gas. The catalyst is contacted with such gas for a time sufficient to increase the chloride level of the catalyst to at least about 1.6 percent, based on the weight of the catalyst. At chloride concentration below this level, secondary burn conditions will produce agglomeration of the iridium. Preferably the concentration of chloride ranges between about 1.6 percent and 2.5 percent, based on the total weight of the catalyst (dry basis). Larger concentrations of chloride on the catalyst are not necessary to adequately protect the catalyst during the high temperature secondary burn. There is a trade off between the time required for adequate chlorination of the catalyst and the hydrogen chloride concentration of the gas used for chloriding the catalyst. Larger hydrogen chloride concentration in the gas thus require less contact time to adequately chlorinate the catalyst, and conversely lower hydrogen chloride concentrations in the gas require greater contact time. For example, at a gas flow rate of 27 SCF/hr/lb of catalyst, a gas containing 1600 vppm of hydrogen chloride will require about 2 hours for chlorination, and a gas containing about 100 vppm of hydrogen chloride will require about 40 hours to accomplish the same amount of chlorination. In chloriding the catalyst, it is generally adequate to use a gas containing the same or about the same concentration of hydrogen chloride as employed in chloriding the catalyst for the low temperature primary burn, though to offset the additional time required to complete chlorination of the catalyst, the concentration of hydrogen chloride can be proportionately increased taking into account the amount of halide to be deposited on the catalyst, and time required to complete the chlorination.
The high temperature secondary burn essentially completely removes the residual coke left from the low temperature primary burn without agglomeration, or increased agglomeration of the iridium component. In conducting the secondary burn, the levels of concentration of the hydrogen chloride and oxygen, respectively, in the gas, added or injected during the secondary burn, are increased as contrasted with the concentration of hydrogen chloride and oxygen employed in conducting the low temperature primary burn. A level of chloride ranging from about 100 vppm to about 5000 vppm chloride, preferably from about 150 vppm to about 3000 vppm chloride has been found effective in suppressing agglomeration of the iridium component during the secondary burn. The gas must also contain oxygen, generally up to about 5000 parts, per million parts by volume of gas (vppm), preferably from about 1000 vppm to about 5000 vppm of oxygen, more preferably from about 2000 vppm to about 4000 vppm of oxygen, this amount of oxygen being sufficient to provide a flame front temperature ranging above about 425.degree. C. to a maximum of about 530.degree. C., preferably from about 480.degree. C. to about 510.degree. C. The reaction time is sufficient for the flame front to pass through the bed of catalyst to effect at least about 90 percent burn off of the residual coke, or coke remaining from the low temperature burn, and preferably essentially complete coke removal (viz., 100 percent), based on the weight of the catalyst, without agglomeration, or increased agglomeration of the iridium component.
In conducting the primary burn, it has thus been found that hydrogen chloride in levels of about 10 vppm to about 100 vppm, preferably about 30 vppm to about 50 vppm, with the required amount of oxygen, are adequate to suppress iridium agglomeration. Occasionally however, it has been found that some iridium agglomeration can occur, e.g., as when the temperature of the primary burn exceeds about 425.degree. F., too much moisture enters the system, or insufficient chloride is present on the catalyst to provide the required passivation. In such event, it has been found that the use in the secondary burn, of about 200 vppm hydrogen chloride, and greater, preferably from about 200 vppm to about 5000 vppm hydrogen chloride, along with the required amount of oxygen, will redisperse agglomerates of iridium that are produced during the primary burn caused by such upsets, or failure to strictly observe the specified regimen of conditions. This level of hydrogen chloride, with the required oxygen, is also adequate to remove all of the carbon from the catalyst. Moreover, in accordance with the more preferred practice of this invention, the oxygen concentration is increased, preferably in step-wise fashion, or linearly, preferably the latter, over the period of the burn to a level ranging from about 2.0 percent to about 5 percent, based on the volume of the gas. By operating in this manner somewhat greater effectiveness is achieved in burning the residual coke from the catalyst. In addition, if the catalyst contains iridium agglomerates, as may have been caused by upsets in the primary regeneration step, the agglomerates are redispersed.
Iridium agglomeration has been found to reduce the metal surface area of the catalyst, this lessening catalyst activity and catalyst activity maintenance (cycle length). Only dispersed iridium can be effective in moderating coke formation and reducing the catalyst deactivation rate; iridium agglomeration, for purposes of the present invention, being defined as the percentage of the total iridium atoms on the catalyst in clusters of 50.ANG., or greater, as measured by x-ray diffraction. If the conditions of the primary and secondary burn steps are carefully observed, there will be essentially no agglomeration of the iridium in burning the coke from the catalyst; in either the primary or secondary burn. An initial relatively low level of hydrogen chloride is incorporated with a coked iridium containing catalyst, optimally in amount sufficient, and at conditions sufficient to passivate the iridium component of the catalyst against agglomeration in the low temperature primary burn which removes a prepondance of the coke without agglomeration of the catalyst. Prior to initiation of the secondary burn, additional hydrogen chloride is added to the catalyst, again (1) in amount sufficient to passivate the iridium component against agglomeration in the higher temperature secondary burn which removes residual coke from the catalyst without agglomeration, or increase in the level of agglomeration, of the iridium component; and (2) in amount sufficient that, at the conditions given, any agglomerates of iridium produced in the low temperature, or primary burn step, via failure to strictly observe the required regimen of conditions, will be redispersed. No chlorine is injected into the process. Corrosion is minimized because the regeneration and reactivation of the catalyst is achieved in an essentially dry system. Reduction of the catalyst is not required.
Excessive chloride is removed from the catalyst by stripping the catalyst from the high temperature secondary burn of chloride by contact thereof with steam at temperature ranging from about 400.degree. C. to about 500.degree. C., preferably from about 470.degree. C. to about 490.degree. C. Preferably, excessive chloride is stripped from the catalyst by use of an admixture of steam and hydrogen chloride, the molar ratio of H.sub.2 O:HCl ranging from about 80:1 to about 20:1, preferably from about 50:1 to about 30:1. The catalyst, after stripping will contain from about 0.8 percent to about 1.3 percent, preferably from about 0.9 percent to about 1.1 percent chloride, based on the weight of the catalyst (dry basis), at which time the regenerated catalyst is ready for use in an operating run for the conversion of a hydrocarbon feed.